You may be right. With stock hubs and 3:5 bead locks the rear is 49" with factory spacers installed on a Moto axle. LSR axles make it 50" with same setup. So being a weird wheel size would make sense but I don't have any moto wheels to verify.
Sloot is correct there and I was mistaken. Just checked my Moto axle setup on one quad again and it's 48" with 3:5 wheels. Had done the same and made spacers as well. So factory beadlocks must be a weird size.